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. . .337
Claude E. Payri
The coral reef communities of Vanuatu have been little studied and nothing has been previously published on the benthic algal flora from Espiritu Santo Island. Some marine algae from Vanuatu have been found in the British Museum collections (BM) and are mainly Sargassum species and Turbinaria ornata. In their report on Vanuatu’s marine resources, Done and Navin (1990) mentioned Halimeda opuntia as occurring in most of the
sites investigated and noted the high encrustation of coralline algae in exposed sites. More work has been done on seagrass communities; earlier authors reported a total of nine species from Vanuatu including
Algal and Seagrass Communities from Santo Island in Relation to Habitat Diversity
Ben
thic
five species from Santo, i.e. Cymodocea rotundata, Halodule uninervis, H. pinifolia, Halophila ovalis and Thalassia hemprechii.
The present algal flora and seagrass investigation of Santo was conducted during August 2006 as part of the "Santo 2006 expedition". This work is a com-panion study to that of the Solomons and Fiji and is intended to provide data for ongoing biogeographic work within the West and Central Pacific.
Extensive surveys have been carried out in most of the habitats recognized in the southern part of Santo Island and in the Luganville area, including islands, shorelines, reef flats, channels and deep outer reef slopes.
The 42 sites investigated are shown in figure 409 and are distributed from Palikolo in the north-ernmost part of the study area, down to Urepala islet located in the southern part including the Segond Channel, the Malo passage and Abokisa Island on the east coast of Aore Island. Sites were selected to include the largest possible range of environments.
Most of the sites were surveyed by SCUBA divers from the surface down to 60 m deep. The shallow areas, including fringing reef flats, reef channels and rocky shorelines, were sampled by snorkelling and walking on the reef. The sampling effort was standardized and inventory duration at each site was fixed to 80 minutes. A species inventory was compiled in order to create a more comprehensive
species list for the southern part of Santo. Specimens were sampled to make a taxonomical collection for the area.
All the collected specimens were pressed and dried for herbaria; fragments of specimens were preserved in a solution of buffered formalin in seawater (5 %) for further anatomical studies. Tissues from vari-ous taxa were also preserved for further phylog-eny and molecular analysis and all the herbarium specimens were air dried (without formalin) which allows for extra DNA analysis if necessary. The collection is currently housed in the phycological herbarium at IRD Nouméa (IRD-NOU) and will be transferred to the Muséum national d’Histoire naturelle in Paris (PC). Part of the collection will be deposited at USP in Suva, Fiji.
Sampling SiteS and methodS
marine macrophyteS in Santo: general inSightS
Macrophyte communities on coral reefs are generally distributed in assemblages that more or less reflect reef zonation. The distribution of the marine flora on a coral reef is influenced by various factors including sunlight, salinity, water turbulence and currents, the nature of the substratum, depth, exposure to air, geo-morphology, topography, herbivore pressure and biological competition with other benthic organisms.
In addition, Vanuatu’s reefs have a complex tec-tonic history, having experienced several emer-gence and subsidence events. These have resulted in some features that are typical of many reefs with rocky shorelines, and recent tectonic dis-placements and uplifts may have affected some of their benthic assemblages. However, we did not observed a recent influence of tectonic dis-placement on benthic communities in the study areas and the most significant disturbances we
in BouChEt P., LE guyadEr h. & PasCaL o. (Eds), The Natural History of Santo. MNhN, Paris; Ird, Marseille; PNI, Paris. 572 p. (Patrimoines naturels; 70).
338. . .
. . . . . . .Marine Ecosystems
observed were the result of recent cyclone activity and bleaching events over the past few years.
However, environmental factors are not homoge-neous across the reefs, and gradually change from the shoreline to outer reef slopes through lagoons and reef flats. The rather patchy zonation patterns
are generally distributed parallel to the shorelines and reef margins.
This synthesis comprises an overview of the rep-resentative biotopes investigated and describes the different macrophyte (algae and seagrasses) commu-nities associated with the different identified habitats.
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98
7
6
5
4
3
2 1
4645 44
43
42
41 4039
38
37
3635
34
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23
22
2120 1918
17
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16
ESPIRITU SANTO
Malo
Aore Tutuba
(Luganville
Coolidge
Abokisa
Paikolo
Million Dollar Point�
Brigstocke
Urelapa
Segond Channel
Bruat Channel
�
Reef geomorphologyOcean-exposed fringing reef
deep terrace
fore reef
reef flat
shallow terrace
( sampling sites
� wrecks
Santo 2006, marine algae habitats
Mainland
main land
Shelf patch-reef complex
subtidal reef flat
Shelf slope
shelf slope
Inner-seas exposed fringing reef
enclosed lagoon or basin
forereef
reef flat
shallow terrace
Inner-seas patch-reef complex
forereef
pinnacle
reef flat
subtidal reef flat
0 2,5 5 km
�
Cartographie : C. Chauvin IRD 2008. Source : Payri Santo 2006, Andréfouët Millenium Coral Reef Mapping Project.
Datum : WGS 1984Projection : UTM Zone 58 S
Figure 409: Map of sampling sites in the Luganville area, southern part of santo Island.
. . . . . . .
. . .339
The Natural History of Santo
The main features of the Santo coral reef complex are the absence of a barrier reef and associated habitats. Most of the structures comprise narrow fringing reefs, outer reefs, patch reefs in shallow water, sheltered and open embayments, deep chan-nels and shallow passes, exposed outer reef slopes and reef walls or drop-offs.
Most of the sites have reef habitats compressed into narrow coastal margins and exposed to ocean influ-ences. On unsheltered coasts the coral reefs are wave-beaten structures that are heavily encrusted by coralline algae as well as by coral species that are well-adapted to strong turbulence.
The great ocean depths, large fetches and the refrac-tion of swells around the small islands adjacent to Santo mean that the open coasts on all sides are subject to strong wave forces, and this limits the types of reefs that can establish. Less robust forms of corals and other benthic communities are however able to develop in more sheltered embay-ments. The islands around the Segond Channel provide significant shelter from the open ocean, and the channel accumulates siltation originating from the terrestrial erosion of the adjacent island of Santo; the channel supports a range of habi-tats with conditions ranging from intermediate to abundant shelter, and muddy substrata.
The 42 sites surveyed have been classified into 12 major habitat groups which include geomorphology, topog-raphy and major benthic communities. Schematic diagrams (profiles) are given in figures 411-422, the list of the symbols used in the profiles are given figure 410. Descriptions of the profiles are as follows.
Segond channel (Fig. 411) …This long channel runs between Santo and Aore Island. Around the Luganville area and down to the south there are few reef formations and coral communities and these are mainly developed on sandy slopes and rubble. Narrow reef flats are present, mostly at both entrances to the Channel and along the Aore Island coast. Coral communities are mostly Acroporidae and occasional massive Porites. There is also evidence of damaged coral in the high proportion of coral rubble. Large beds of the green macrophyte Halimeda opuntia intermixed with sponges colonise the hard substratum. In the northern area, the middle part of the channel is deep (70 m depth) and muddy, marked with ghost shrimp (Calianasseae) hummocks and small benthic communities including some Nephtheidea, Dophleina and Asthenosoma urchins. The benthic communities of the channel environment are dominated by sponges and octocorallians (soft corals and sea fans). On the shallow muddy flats adjacent to the shore of Santo island seagrasses such as Halodule and Cymodocea form sparse patches.
repreSentative biotopeS
Figure 410: List of symbols used for figures 411-422.
Living massive coral
Living branched coral
Living tabular coral
Living foliaceous coral
Gorgonian
Seagrass
Sponges
Rhodophyta
Dead corals
Coral rubble
Ghost shrimp hummock
Coconut tree
Trees
Native houses
Tubastrea
Sarcophyton
Lobophyton
Halimeda
Caulerpa
Mangrove
340. . .
. . . . . . .Marine Ecosystems
shoreline
Depth (m)
Dis
tanc
e fr
om s
hore
(m
)
Depth (m)
Sant
o Is
.A
ore
Is.
Sego
nd C
hann
el
0 10 20 30 40 50
0 10 20 30 40 50
018
00
mudflats and mangrove
seag
rass
bed
outw
ard
chan
nel s
lope
chan
nel b
otto
min
war
d ch
anne
l slo
pe
Figu
re 4
11: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
the
sego
nd C
hann
el.
a: M
angr
ove
tree
s on
the
shor
elin
e. b
: typ
ical
gen
tle s
lope
with
den
se H
alim
eda
bed.
c: t
ypic
al m
ixed
com
mun
ity o
n ch
anne
l slo
pe d
omin
ated
by
Nei
phte
idae
. d: d
iffus
e se
agra
ss b
ed o
f Hal
odul
e pi
nifo
lia a
nd
Hal
ophi
la o
valis
. e: H
alim
eda
min
ima
form
ing
thic
k m
ats
with
spo
nges
and
oth
er o
rgan
ism
s on
the
chan
nel s
lope
. F: t
ypic
al c
omm
unity
of i
nver
tebr
ates
and
alg
ae o
n th
e de
ep c
hann
el e
dge.
g: M
ixed
sea
gras
s be
d of
Hal
odul
e un
iner
vis
and
Cym
odoc
ea s
erru
lata
. h: P
hyso
gyra
. i: g
orgo
nian
Jun
cella
. J: F
rom
ia m
illep
rore
lla. K
: Dop
hlei
na. l
: Gom
ophi
a w
atso
ni. (
Phot
os J
.-L. M
enou
& J
.-M. B
oré
Ird
Nou
méa
).
aB
C
dE
F
g
h
JK
I
L
. . . . . . .
. . .341
The Natural History of Santo
Figu
re 4
12: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
Cha
nnel
Pas
s (s
outh
ern
entr
ance
of
the
sego
nd C
hann
el).
a: B
ranc
hing
Acr
opor
a co
mm
unity
on
chan
nel
slop
e. b
: typ
ical
Hal
imed
a be
ds o
n th
e ed
ge o
f th
e sl
ope.
c: r
ubbl
e of
Acr
opor
a br
anch
es. d
: gor
goni
an. e
: Elli
sella
. F: P
hyllo
spon
gia
lam
elos
a w
ith
Hal
imed
a. g
: Hal
imed
a m
inim
a. h
: Crin
oids
Com
anth
eria
bria
reus
and
Com
anth
us b
enne
tti. i
: Cho
riast
er g
ranu
latu
s. J:
Tub
ipor
a m
usic
a. K
: The
leno
ta a
nax.
(Ph
otos
J.-L
. Men
ou &
J.-M
. Bor
é Ir
d N
oum
éa).
a
dB
C
EF
rock
y re
ef fl
atou
twar
d ch
anne
l slo
pech
anne
l bot
tom
inw
ard
chan
nel s
lope
reef flat
Dis
tanc
e fr
om s
hore
(m
)
Sant
o Is
.A
ore
Is.
Sego
nd C
hann
el0
650
Depth (m)
0 10 20 30 40
Depth (m)
0 10 20 30 40
g
hJ
I K
342. . .
. . . . . . .Marine Ecosystems
the delicate paddle seagrasses Halophila spp. were observed on the sandy slope down to 50 m deep. Sparse coral blocks and rubble are the main features from the top down to the mid-slope while coarse sand and debris are dominant further down beyond 30 m deep. Species diversity is low except for star-fish and holothurians with various species such as Nardoa gomophia, Echinaster callosus, Choriater granulatus, Holothuria (Microthele) fuscogilva and M. fuscopunctata and the red algae that display several gelatinous species in the deeper part of the slope.
Sheltered embayment (palikolo bay) …(Fig. 416)
From shore to open ocean, this bay contains sev-eral biotopes including:
• Prolific seagrass beds in the fringing muddy flats intermixed with a green macroalgal com-plex of Halimeda and Caulerpa;• Shallow sheltered reefs on sand dominated by acroporids;• Large areas of coral-construction on deeper (6 m) patch reefs;• A steep slope from 15 m down to 60 m deep. The patch reefs here support a high diversity of species with a very rich coral community including many fungids and octocorallians. Large mounds of rubble covered by the brown alga Lobophora variegata indicate an accumula-tion of coral skeleton fragments that have bro-ken in recent decades. The diversity decreases down the slope; some holothurians including Thelenota anax and Neoferdina cumingii (50 m) have been observed along with green algae Cladophora and Halimeda in the deeper zone.
open embayment, partially …sheltered (east aore) (Fig. 417)
This habitat occupies the north eastern part of Aore Island. The coral community is developed on a gen-tle sandy slope down to 25 m deep and looks like the silty bottom of a lagoon. Porites with abundant soft corals, sponges and various branching Acropora form large beds down to 15 m deep. Various coral-line and red fleshy algae were recorded on hard sub-strata. Corals such as Polyphyllia, Herpolitha limax, Sandalolitha robusta and Cynarina lacrymalis were also observed in these sheltered areas. The accumu-lation of fine carbonate sand in the deeper part is a typical characteristic of lagoons and supports large patches of mixed green algae including Halimeda, Udotea, Avrainvillea and Caulerpa. Visibility was reduced in this environment due to the abundance of fine carbonate particles in the water column.
Sheltered fringing reef (West …tutuba island) (Fig. 418)
On the west side of Tutuba Island adjacent to the beach there is a narrow and patchy fringing reef front-ing in some places an enclosed lagoonal gutter (10 m deep) and then a gentle outer slope that nonetheless
channel pass (southern entrance …of Segond channel) (Fig. 412)
The topography and the environment of the Segond Channel changes from the north to the south with the increasing current. The coral communities are well developed on the slopes with massive corals in the shallow areas while a rich branched coral com-munity is associated with green calcareous algae Halimeda opuntia and the coralline algae Amphiroa on the gentle sandy slope. The bottom of the chan-nel is a hard substratum supporting large coral patches with flourishing communities of benthic invertebrates including octocorallians and numer-ous crinoids. This area experiences strong tidal currents. The reef flat on the Aore side is narrow with a steep slope dominated by Halimeda mac-roloba anchored in the muddy sand and various red algae entangled in dead Acropora branches.
Sheltered fringing reef …(brigstocke point, SW luganville) (Fig. 413)
Most of the reefs fringing the southern corner of Santo are characterized by a narrow area of subti-dal grooves adjacent to the rocky shoreline, with dense macroalgal vegetation of red algae Callophycus spp, Portieria hornemanii and Amphiroa crassa. The slopes are mostly covered with coral debris with some large blocks of dead Porites. The green calcareous alga Halimeda opuntia develops spectacular beds from 15-30 m deep, while Halimeda macroloba and the red foliaceous algae belonging to the Peyssonneliaceae form aggregations (soft nodules) up to 10 cm in diam-eter that are locally abundant on the top of the slope.
malo water passage (between aore …and malo islands) (Fig. 414)
The Aore site is fringed by small Rhizophora clumps that grow on the beaches along a narrow and shal-low depression where Acroporids and the seagrass Enhalus acoroides are well developed on sand flats with moderate tidal currents. The shallow reef flat on the side of the islet is covered with many massive Porites; on the side of Malo Island the reef is deeper and the corals are more massive and have developed into large patches with abundant encrusting coral-line algae. The coral cover is high on the reef slope along the water passage. Foliose and branched corals are abundant on the reef slopes while they decrease further down to the bottom of the passage where strong currents limit the development of a benthic community. Large spurs parallel to the sea floor that support octocorallians are the main feature of the base of the slope on the Malo side.
Sheltered sandy slope (malo passage) …(Fig. 415)
The Malo passage has typical sandy slopes with little reef formation along the shores of Aore and Malo islands. Fringing reef flats are narrow, shallow and protected. No seagrass beds were found, only
. . . . . . .
. . .343
The Natural History of Santo
Figu
re 4
13: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
a sh
elte
red
frin
ging
ree
f (B
rigst
ocke
poi
nt, s
W L
ugan
ville
).a
: Hal
imed
a be
ds o
n th
e ge
ntle
sand
y slo
pe. b
: Cal
loph
ycus
serr
atus
. c: B
ranc
hed
cora
lline
alg
ae. d
: Hal
imed
a di
stor
ta o
n sa
ndy b
otto
m. e
: Bra
nchi
ng co
ral c
omm
unity
. F: B
all-l
ike
Peys
sonn
elia
ceae
. g: T
hele
nota
an
ax. (
Phot
os J
.-L. M
enou
& J
.-M. B
oré
Ird
Nou
méa
).
reef
flat
reef
slo
pew
ith la
rge
stan
d of
Hal
imed
asa
ndy
bott
om
Dis
tanc
e fr
om s
hore
(m
)Sa
nto
Is.0
100
Depth (m)
0 10 20 30
Depth (m)
0 10 20 30
a
dC
B
g
FE
344. . .
. . . . . . .Marine Ecosystems
Figu
re 4
14: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
the
Mal
o pa
ssag
e (b
etw
een
aore
and
Mal
o Is
land
).a
: Flo
uris
hing
com
mun
ity o
n th
e ha
rd c
hann
el b
otto
m. b
: spu
rs a
t th
e to
p of
the
ree
f sl
ope.
c: B
ranc
hing
cor
als
on t
he r
eef
flat.
d: S
tero
neph
tya.
e: r
eef
slop
e co
mm
unity
com
pose
d of
bra
nchi
ng a
nd
mas
sive
cor
als.
F: s
eagr
ass
Enha
lus
acor
oide
s. g
: Agl
aoph
enia
. h
: gor
goni
an c
omm
unity
on
the
bott
om o
f th
e re
ef s
lope
. i:
Can
dle-
like
cora
lline
alg
ae o
n th
e re
ef e
dge.
J: M
assi
ve c
oral
s K
: Bra
nchi
ng
Acro
pora
and
sea
gras
s co
mm
unity
in t
he m
oat.
(Pho
tos
J.-L.
Men
ou &
J.-M
. Bor
é Ir
d N
oum
éa).
lago
onde
pres
sion
/moa
tis
let
frin
ging
ree
fw
ater
pas
sage
reef
flat
Dis
tanc
e fr
om s
hore
(m
)
Aor
e Is
.M
alo
Is.
Mal
o Pa
ssag
e0
1850
Depth (m)
Depth (m)
0 10 20 30
0 10 20 30
aB
Ed
c
F
K
Jg
hI
. . . . . . .
. . .345
The Natural History of Santo
Figu
re 4
15: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
a sh
elte
red
sand
y sl
ope
(Mal
o Pa
ssag
e).
a: t
ypic
al m
ixed
bed
s of
Hal
imed
a cy
lindr
acea
and
Hal
ophi
la o
valis
. b
: san
dy s
lope
. c:
Str
ombu
s lu
huan
us o
n sh
allo
w s
andy
bot
tom
. d
: Rhi
pilia
cra
ssa
on r
ubbl
e. e
: sof
t co
ral
on s
andy
bot
tom
. F:
hol
othu
rian
on ru
bble
on
the
uppe
r par
t of t
he s
lope
. g: M
etal
ia s
tern
alis
. h: G
ibsm
ithia
haw
aiie
nsis
on
deep
rubb
le. i
: Phy
llosp
ongi
a la
mel
osa.
J: s
pong
e M
elop
hlus
. K: D
icho
tom
aria
mar
gina
ta. (
Phot
os
J.-L.
Men
ou &
J.-M
. Bor
é Ir
d N
oum
éa).
sand
y sh
allo
w r
eef f
lat
reef
slo
pew
ith r
ubbl
e an
d co
ral p
atch
es
deep
reef
slo
pew
ith r
ubbl
e
Dis
tanc
e fr
om s
hore
(m
)A
ore
Is.
300
0
Depth (m)
0 10 20 30 40 50
Depth (m)
0 10 20 30 40 50
a C
E
d F IJ
B
gh
K
346. . .
. . . . . . .Marine Ecosystems
Figu
re 4
16: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
a sh
elte
red
emba
ymen
t (P
alik
olo
Bay
).a
: In
vert
ebra
te a
ssem
blag
e on
dea
d co
rals
. b:
Dis
ticho
pora
. c:
dee
p sa
ndy
bott
om w
ith m
assi
ve c
oral
pat
ches
. d:
Cym
odoc
ea s
erru
lata
(la
rge)
mix
ed w
ith H
alod
ule
univ
ersi
s. e
: Ty
dem
ania
exp
editi
onis
. F:
sof
t co
ral R
umph
ella
agg
rega
ta. g
: rub
ble
cove
red
by L
obop
hora
var
iega
ta. h
: Hal
imed
a m
acro
loba
gro
win
g am
ong
cora
ls o
n sa
ndy
bott
om. i
: Fun
gids
gro
win
g am
ong
rubb
le. J
: Bra
nchi
ng a
crop
ora
com
mun
ity o
n sh
allo
w r
eef
flat.
K: M
assi
ve c
oral
s ho
usin
g lu
xuria
nt o
ctoc
oral
lian
faun
a. l
: Mas
sive
cor
al o
n th
e sl
ope.
m: T
hele
nota
ana
x. (
Phot
os J
.-L. M
enou
& J
.-M. B
oré
Ird
Nou
méa
).
Sant
o Is
.Pa
likol
o B
ay
man
grov
ese
agra
ss b
ed
Halimeda bed withbranching Acropora
reef
flat
patc
h re
efre
ef s
lope
Dis
tanc
e fr
om s
hore
(m
)0
450
Depth (m)
Depth (m)
0 10 20 30 40 50 60
0 10 20 30 40 50 60d
h
M
C L
E
i
KJ
g
Ba F
. . . . . . .
. . .347
The Natural History of Santo
Figu
re 4
17: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
an o
pen
and
part
ially
she
ltere
d em
baym
ent
(eas
t ao
re).
a: s
pong
es g
row
ing
amon
g ru
bble
on
the
uppe
r slo
pe. b
: hol
othu
rian
Boha
dchi
a gr
aeffe
i. c:
red
alg
ae T
itano
phor
a an
d Pa
dina
. d: s
andy
lago
on fl
oor.
e: P
olyp
hylla
. F: B
ranc
hing
Acr
opor
a. g
: Hal
imed
a an
d Pa
dina
on
gen
tle s
andy
slo
pe. h
: spo
nge
Phak
ellia
cav
erno
sa. i
: Fun
gids
gro
win
g am
ong
rubb
le. J
: Aca
ntha
ster
pla
ncii
feed
ing
on c
oral
. K: g
reen
alg
ae U
dote
a ar
gent
ea. (
Phot
os J
.-L. M
enou
& J
.-M. B
oré
Ird
Nou
méa
).
A
frin
ging
ree
fsh
allo
w r
eef
alga
l bed
on s
andy
and
rub
ble
bott
om
Dis
tanc
e fr
om s
hore
(m
)A
ore
Is.
Depth (m)
0 10 20 30
Depth (m)
0 10 20 301
850
0
B
EI
F J
G
C
D H K
348. . .
. . . . . . .Marine Ecosystems
Figu
re 4
18: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
a sh
elte
red
frin
ging
ree
f (t
utub
a Is
land
W).
a: M
ixed
Acr
opor
a an
d H
alim
eda
com
mun
ity. b
: att
ract
ive
cora
l com
mun
ity. c
: spo
nge
Lios
ina,
abu
ndan
t on
hard
cor
als.
d: H
olot
huria
edu
lis o
n th
e flo
or. e
: sof
t cor
als.
F: L
arge
bra
nchi
ng A
crop
ora.
g: M
ixed
as
sem
blag
e of
sof
t an
d ha
rd c
oral
s. h
: Hal
imed
a m
inim
a on
dee
p re
ef s
lope
. i: t
abul
ar A
crop
ora.
(Ph
otos
J.-L
. Men
ou &
J.-M
. Bor
é Ir
d N
oum
éa).
seag
rass
bed
internal channel
reef
flat
reef
slo
pesa
ndy
bott
om
Dis
tanc
e fr
om s
hore
(m
)0
Depth (m)
0 10 20 30 40 50
0 10 20 30 40 5041
0
Depth (m)
AB
C
D
EF
GH
I
. . . . . . .
. . .349
The Natural History of Santo
Figu
re 4
19: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
a w
indw
ard
frin
ging
ree
f an
d ex
pose
d ou
ter
reef
slo
pe (
tutu
ba Is
. N &
E).
a:
spur
s. b
: to
p of
ree
f. c:
typ
ical
ree
f ed
ge c
omm
unity
com
pose
d of
mas
sive
and
tab
ular
cor
als.
d:
Cul
cita
nov
aegu
inea
. e:
Cau
lerp
a fe
rgus
oni.
F: r
ed a
lgae
Pre
daea
lac
inio
sa.
g:
Cor
allin
e al
gae.
h
. Hal
imed
a on
rub
ble.
i: o
ctoc
oral
lian
com
mun
ity o
n sp
ur e
dges
. J: C
rinoi
d as
sem
blag
e. K
: spo
nge
Mel
ophl
us. l
: abu
ndan
t la
rge
spon
ges.
m: o
ctoc
oral
lian
com
mun
ity o
n th
e re
ef e
dge.
n: H
elio
pora
on
slop
e. o
: Lux
uria
nt c
oral
com
mun
ity o
n m
id s
lope
. p: M
assi
ve c
oral
s on
slo
pe in
dee
p w
ater
. Q: g
reen
alg
a C
lado
phor
a ob
ukho
ana
on c
oars
e sa
nd. (
Phot
os J
.-L. M
enou
& J
.-M. B
oré
Ird
Nou
méa
).
Dis
tanc
e fr
om s
hore
(m
)
Depth (m)
Depth (m)
50403020100
50403020100
045
0
reef
flat
spur
sre
ef fr
ont
reef
slo
pede
ep b
otto
m w
ith m
assi
ve c
oral
s
AB
CD
E
L
F
KJ
IH
G
MN
OP
Q
350. . .
. . . . . . .Marine Ecosystems
Figu
re 4
20: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
an o
uter
ree
f pl
atfo
rm (
Mal
o Is
. W c
oast
).a
: ree
f pl
atfo
rm. b
: Aca
ntha
ster
pla
ncii.
c: L
arge
tab
ular
Acr
opor
a. d
: gor
goni
an. e
: rub
ble.
F: C
ulci
ta n
ovea
guin
ea. (
Phot
os J
.-L. M
enou
& J
.-M. B
oré
Ird
Nou
méa
).
Dis
tanc
e fr
om s
hore
(m
)
Depth (m)
Depth (m)
0
0 10 20 30 40 50 60
0 10 20 30 40 50 60re
ef s
lope
frin
ging
ree
fpl
atfo
rmre
ef e
dge
A BC
D
F
E
1 20
0
. . . . . . .
. . .351
The Natural History of Santo
Figu
re 4
21: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
a pa
tch
reef
and
out
er s
lope
adj
acen
t to
a li
mes
tone
isla
nd (
abok
isa
Isla
nd).
a: a
ttra
ctiv
e co
ral c
omm
unity
on
the
reef
flat
. b: H
alim
eda
cylin
drac
ea o
n sh
allo
w s
andy
bot
tom
. c: B
ranc
hing
Acr
opor
a on
sha
llow
san
dy b
otto
m. d
: Mas
sive
tab
ular
and
bra
nchi
ng c
oral
s. e
: Mas
sive
cor
al
head
s on
san
dy b
otto
m.
F: t
abul
ar A
crop
ora
com
mun
ity o
n pa
tch
reef
. g
: Li
ncki
a gu
ild.
h:
Thel
enot
a ru
brol
inea
ta.
i: B
ranc
hing
Acr
opor
a on
san
dy s
lope
. J:
Bra
nchi
ng A
crop
ora
on s
lope
. K
: C
horia
ster
gr
anul
atus
. l: G
ibsm
ithia
haw
aiie
nsis
. m: M
assi
ve c
oral
com
mun
ity o
n th
e te
rrac
e. n
: sof
t cor
als
on m
assi
ve c
oral
hea
d. o
: Pre
daea
wel
dii.
p: H
olot
huria
( M
icro
thel
e) fu
scog
ilva.
Q: g
orgo
nian
on
the
bott
om
of t
he o
uter
slo
pe. r
: Hal
imed
a cy
lindr
acea
and
Hal
ophi
la o
valis
on
deep
san
dy b
otto
m. (
Phot
os J
.-L. M
enou
& J
.-M. B
oré
Ird
Nou
méa
).
reef
slo
pete
rrac
e
rocky reef flat
isle
t
fringing reef
reef
slo
pede
ep r
eef s
lope
with
detr
itic
accu
mul
atio
n
Depth (m)
Depth (m)
Dis
tanc
e (m
) 50403020100
50403020100
095
0
A IE M
LQH
D
B
C
FG
K
J NRP
O
deep
ree
f slo
pe
352. . .
. . . . . . .Marine Ecosystems
Figu
re 4
22: s
chem
atic
dia
gram
of
the
topo
grap
hy a
nd r
eef
com
mun
ities
of
reef
wal
l (u
rela
pa Is
land
).a
: typ
ical
out
er s
lope
at 3
0 m
dep
th. b
: Bra
nchi
ng A
crop
ora
com
mun
ity o
n th
e sa
ndy
terr
ace.
c: t
op o
f the
reef
. d: D
iplo
astr
ea h
elio
pora
. e: r
eef s
lope
and
wal
l. F:
Fol
iace
a co
ral c
f. Tu
rbin
aria
. g: F
olia
ceou
s co
rals
on
the
wal
l. h
: Pac
hysi
ris s
peci
osa.
i: A
crop
ora
rubb
le o
n th
e re
ef c
rest
. J: M
onta
stre
a an
nulig
era.
K: C
eler
ina.
l: A
ster
onem
ia a
nast
omos
ans.
m: g
orgo
nian
and
crin
oids
on
the
drop
-off.
n: C
oral
line
alga
e an
d oc
toco
ralli
an o
n th
e w
all 2
. o: H
alim
eda
min
ima
on ru
bble
. p: A
crop
ora
on s
andy
bot
tom
with
ripp
le m
arks
. Q: P
eyss
onne
lia. r
: Cry
ptic
com
mun
ity o
f cor
allin
e al
gae
on th
e ou
ter s
lope
. S: C
oral
gal
(cor
al-a
lgal
) as
sem
blag
e on
the
ree
f sl
ope.
t: M
assi
ve b
ranc
hing
Acr
opor
a on
the
ree
f fla
t. U
: gor
goni
an o
n th
e dr
op-o
ff (w
all)
. (Ph
otos
J.-L
. Men
ou &
J.-M
. Bor
é Ir
d N
oum
éa).
Dis
tanc
e (m
) 0
320
Depth (m)
Depth (m)
50403020100 60
50403020100 60
fringing reef
isle
t
gentle wall
ED
JK
PQ
R
L
U
T
O
S
AB
C IF NH
MG
reef
slo
pefr
ingi
ng r
eef
reef
slo
pe
stee
p w
all o
r dr
op o
ff
. . . . . . .
. . .353
The Natural History of Santo
goes down to 50 m in depth. The reef flat area is very shallow and supports a diffuse seagrass bed com-posed mainly of Cymodocea serrulata, intermingling with algae and small coral colonies. The front of the stretches of reef and edges of the lagoon are overgrown by a dense covering of erect soft corals such as Sinularia and Sarcophyton, while the narrow silty lagoon con-tains isolated massive Porites. The steep internal slope and the outer reef flat are covered by thick swathes of rubble without coral communities. This entire zone is exposed at low tide. The outer reef slope is similar to other sheltered slopes with large areas of broken Acropora branches and plates on white coral sand down to 8 m deep; further down there is an accumulation of coral branches and other carbonate debris with few coral colonies and occasional fleshy algae.
In the area outside the lagoonal depression the sandy bottom supports a mosaic of patch reefs dominated by robust massive corals that are highly dissected with spectacular communities of green and red algae. Several Holothuria edulis have been observed on the shallow sandy bottom.
Windward fringing reef and …exposed outer reef slope (north and east tutuba island) (Fig. 419)
On the windward side, fringing reefs are deeply dis-sected with massive spurs and narrow grooves from 3 to 12 m deep that are littered with coarse sand and coral rubble. Heavy crusts and candle-like coralline algae are well developed in this exposed area along with numerous small species in the overhangs and reef interstices. Corals are sparse on the reef top and mostly consist of massive Pocillopora, Acropora and Millepora. The outer slope is steep from 15 to 30 m in depth, with scattered low spurs and large patches of coarse sand with abundant Halimeda segments. Beautiful sea fans and other octocoral-lian fauna are present on the top of the reef with numerous crinoids making this a very attractive area. From 30-60 m deep the slope is less steep and comprises rubble and scattered coral heads. The deeper part of this seaward slope is typical of many deep slopes, especially with respect to the associ-ated red gelatinous algae (Predaea, Dudresnaya and Gibsmithia), green algae Caulerpa fergusonii and Cladophora ohkuboana and C. dotyana.
The reef slopes facing the open sea are less steep from 30 m down to at least 50 m deep. Coral cover is reduced; Halimeda minima coverage is high and contributes to sand accumulation from their cal-cified segments. Seriatopora cf histrix, and black coral Cirrhipathes anguineus have been observed at 45 m deep.
outer reef platform …(west coast of malo island) (Fig. 420)
Reef formation on the northwest coast of Malo Island provides an example of a platform that was
not seen elsewhere during the survey. This reef is totally subtidal with broad, irregular and meander-ing spurs and grooves. The site has a high proportion of rubble and corals that have been dead for several years. The coral communities were dominated by plate and branching forms. At the time of the survey coral recovery was observed with several living colo-nies of the same size (20-30 cm in diameter). The inshore reef and outer slopes were not studied.
Numerous Culcita novaeguineae were observed, along with one specimen of Acanthaster planci.
patch reef and outer slope adjacent …to limestone island (abokisa island) (Fig. 421)
The small limestone islet located between the larger Tutuba Island and Aore is surrounded by an intermittent fringing reef developed on coral sand to about 6 m in depth with an attractive coral com-munity. Structurally they are dominated by stands of Acropora in plate (A. danai) and branched forms, both living and dead. The dead skeletons provide the substrata for a complex and beautiful coral community in shallow sandy water and include coralline algae. The adjacent slope is dominated by massive Porites down to 15 m deep with numer-ous Halimeda and encrusted rubble as well as rare echinoderms such as Holothuria (Microthele) fuscogilva and Linckia guildingi. Further down the slope drops off to 40 m deep in the north and more than 60 m on the southwestern side with a steeper declination. The coral community is replaced by rubble and a few small colonies (< 1 m high). In deep water, species diversity is low with some red gelatinous algae (Predaea and Gibsmithia), the green algae Caulerpa and Cladophora ohkuboana and the echinoderms Choriaster granulatus and Thelenota rubrolineata.
reef wall (Urelapa island) (Fig. 422) …Fringing reefs on limestone islands adjacent to deep water such as Urelapa and Tuvana islets located off the southern part of Santo have verti-cal underwater cliffs. These reef walls are distinct features that represent one of the more spectacular biotopes for species diversity. Stretches of fringing reef are found adjacent to limestone and coral sand beaches, which change gradually to a reef slope dominated by a mixture of massive corals such as Diploastrea, Goniastrea and Montastrea magnistel-lata and branching Acroporidae down to the cliff precipice. The coral walls start beyond 20 to 25 m deep down at least 60 m deep and are present around the islets where the coast is neither shel-tered nor exposed. Coralline algae in association with numerous fleshy red algae (large patches of Halichrysis irregularis and Asteromenia anastomo-sans) are dominant components with octocoral-lians. Corals are encrusting or foliaceous such as Pachyseris speciosa.
354. . .
. . . . . . .Marine Ecosystems
class rhodophyta
Order Bonnemaisoniales
Family Bonnemaisoniaceae Asparagopsis taxiformis (Delile) Trevisan
Order Ceramiales
Family CeramiaceaeAglaothamnion boergesenii(Aponte & D.L. Ballantine)L’Hardy-Halos & Rueness
Anotrichum tenue (C. Agardh) Nägeli
Antithamnionella elegans(Berthold) J.H. Price & D.M. John
Balliella repens Huisman & Kraft
Centroceras clavulatum(C. Agardh) Montagne
Centroceras minutum Yamada
Ceramium flaccidum(H.E. Petersen) Furnari & Seiro
Ceramium marshallense Dawson
Ceramium upolense South & Skelton
Corallophila apiculata(Yamada) R. Norris
Griffithsia heteromorpha Kützing
Haloplegma duperreyi Montagne
Monosporus indicus Børgesen
Spyridia hypnoides(Bory de Saint-Vincent) Papenfuss
Tiffaniella saccorhiza (Setchell & Gardner) Doty & Menez
table 37: List of rhodophyta, Chlorophyta and Phaeophyceae species from santo waters.
repreSentative macrophyteS commUnitieS
algal vegetation …The species list of the benthic marine algae and sea-grasses collected from Santo is shown in tables 37 & 38. The classification follows The catalogue of the benthic marine algae of the Indian Ocean by Silva and coauthors (1996). The 271 listed species of algae con-sist of 163 Rhodophyta (red algae), 83 Chlorophyta (green algae) and 25 Pheaophyceae (brown algae). A selection of species is illustrated in figures 423-428. About 150 specimens of coralline algae are under study and are not included in this work; only the most common encrusting coralline algae are consid-ered here. The species belong to 12 orders and 45 families (Figs 429 & 430). Most of the specimens have been identified to species level and these repre-sent 90 % of the collection; the 10 % remaining uni-dentified species comprise taxa that could be new to science. Among the identified species, three of them are newly described from Solomon Islands, Fiji and New Caledonia; while at least five taxa including four species of Martensia, Rhizophyllis, Rhodymenia, Hypoglossum and Dudresnaya and one new genus
belonging to the Dumontiaceae are being studied to describe new taxa or establish them as belonging to existing species. The study of the coralline algae will probably reveal new taxa as well.
The algal flora is typically tropical and most of the spe-cies belong to the Indo-Pacific biogeographic province. Comparison with flora from adjacent archipelagos is limited due to the difference in sampling effort in the various regions. However, 55 % and 53 % of the species of Santo are present in Solomons and Fiji respectively.
The Rhodymeniaceae Asteronemia pseudocoalescens described from Lord Howe Island was observed for the first time outside of its type locality, suggest-ing that its geographic distribution is broader than originally thought; this discovery enhances the known biogeographic affinities of the Santo marine flora with the tropical west Pacific.
Algal assemblages are characterized within the biotopes as shown in the following sections.
Wrangelia argus Montagne
Wrangelia elegantissima R.E. Norris
Family DasyaceaeDasya anastomosansWeber-van Bosse
Dasya baillouviana(S.G. Gmelin) Montagne
Dasyphila plumarioides Yendo
Heterosiphonia crispella(C. Agardh) M.J. Wynne
Thuretia sp. nov.
Family DelesseriaceaeFrikkiella searlesiiM.J. Wynne & C.W. Schneider
Haraldia lenormandii(Derbès & Solier) Feldmann
Hypoglossum simulansM.J. Wynne, Price & Ballantine
Martensia cf. australis Harvey
Martensia elegans Hering
Martensia flabelliformeHarvey ex J. Agardh
Martensia fragilis Harvey
Martensia sp. nov.
Myriogramme melanesiensisN'Yeurt, Wynne & Payri
Nitophyllum adhaerens M.J. Wynne
Vanvoorstia spectabilis Harvey
Family Rhodomelaceae Acanthophora pacifica (Setchell) Kraft
. . . . . . .
. . .355
The Natural History of Santo
Acanthophora spicifera(Vahl) Børgesen
Amansia rhodantha (Harvey) J. Agardh
Bostrychia tenella(J.V. Lamouroux) J. Agardh
Chondria armata (Kützing) Okamura
Chondria dangeardii Dawson
Chondria minutula Weber-van Bosse
Chondria ryukyuensis Yamada
Chondria simpliciusculaWeber-van Bosse
Chondria bullata N'Yeurt & Payri
Chondria sp.
Chondrophycus parvipapillatus(C.K. Tseng) Garbary & Harper
Chondrophycus succisus(A.B. Cribb) K.W. Nam
Exophyllum wentii Weber-van Bosse
Herposiphonia nuda Hollenberg
Herposiphonia tenella(C. Agardh) Ambronn
Laurencia brachyclados Pilger
Laurencia cf. distichophylla J. Agardh
Laurencia decumbens Kützing
Laurencia sp. 1
Laurencia sp. 2
Neosiphonia apiculata(Hollenberg) Masuda & Kogame
Polysiphonia scopulorum Harvey
Polysiphonia sertularioides(Grateloup) J. Agardh
Polysiphonia sp
Polysiphonia triton P.C. Silva
Spirocladia barodensis Børgesen
Tolypiocladia glomerulata(C. Agardh) F. Schmitz
Order Corallinales
Family Corallinaceae Amphiroa anceps (Lamarck) Decaisne
Amphiroa crassaLamouroux in Quoy & Gaimard
Amphiroa foliaceaLamouroux in Quoy & Gaimard
Amphiroa fragilissima(Linnaeus) Lamouroux
Amphiroa sp. nov.
Amphiroa tribulus (Ellis & Solander) Lamouroux
Amphiroa valonioides Yendo
Cheilosporum acutilobum (Decaisne) Piccone
Cheilosporum spectabile Harvey ex Grunow
Hydrolithon onkodes(Heydrich) D. Penrose & Woelkerling
Hydrolithon orthoblastum
Hydrolithon reinboldii (Weber-van Bosse & Foslie) Foslie
Jania adhaerens Lamouroux
Jania rubens (Linnaeus) Lamouroux
Lithophyllum pygmaeum(Heydrich) Heydrich
Lithothamnion proliferum Foslie
Neogoniolithon fosliei(Heydrich) Setchell & mason
Order Gelidiales
Family GelidiaceaeGelidiella acerosa(Forsskål) Feldmann & G. Hamel
Gelidium cf. crinale (Turner) Gaillon
Gelidium isabelae W.R. Taylor
Pterocladiella sp.
Order Gigartinales
Family CaulacanthaceaeCaulacanthus ustulatus(Turner) Kützing
Family Corynocystaceaea Corynocystis prostrata G.T. Kraft
Family DicranemataceaePinnatiphycus menouanaN'Yeurt, Payri & Gabrielson
Family DumontiaceaeDudresnaya capricornicaRobins & Kraft
Dudresnaya hawaiiensis R.K.S. Lee
Dudresnaya sp. nov.
Dumontiaceae gen. nov.
Gibsmithia dotyi Hoyle
Gibsmithia hawaiiensis Doty
Gibsmithia larkumii Kraft
Family Hypneaceae Hypnea cervicornis J. Agardh
Hypnea nidulans Setchell
Hypnea pannosa J. Agardh
Hypnea saidana Holmes
356. . .
. . . . . . .Marine Ecosystems
Hypnea spinella (C. Agardh) Kützing
Hypnea valentiae (Turner) Montagne
Family Nemastomataceae Predaea laciniosa Kraft
Predaea weldii Kraft & I.A. Abbott
Family PeyssonneliaceaePeyssonnelia cf. boergeseniiWeber-van Bosse
Peyssonnelia inamoena Pilger
Peyssonnelia sp. 1
Peyssonnelia sp. 2
Family RhizophyllidaceaPortieria hornemannii(Lyngbye) P.C. Silva
Rhizophyllis sp. nov.
Family Schizymeniaceae Titanophora weberae Børgesen
Family Solieriaceae Callophycus densus (Sonder) G.T. Kraft
Callophycus serratus(Harvey ex Kützing) P.C. Silva
Eucheuma horizontaleWeber-van Bosse
Eucheuma sp.
Meristotheca procumbensP. Gabrielson & Kraft
Wurdemannia miniata(Sprengel) Feldmann & G. Hamel
Order Gracilariales
Family Gracilariaceae Gracilaria dotyi Hoyle
Gracilaria sp.
Order Halymeniales
Family HalymeniaceaeCryptonemia cf. lomation(Bertoloni) Agardh
Cryptonemia cf. umbraticola Dawson
Cryptonemia crenulata(J. Agardh) J. Agardh
Cryptonemia umbraticola Dawson
Grateloupia ovataWomersley & J.A. Lewis
Halymenia maculata J. Agardh
Halymenia porphyraeformis Parkinson
Halymenia stipitata I.A. Abbott
Prionitis angusta (Okamura) Okamura
Order Halymeniales
Family Sebdeniaceae Sebdenia cerebriformis N'Yeurt & Payri
Sebdenia flabellata Zablackis
Order Nemaliales
Family Galaxauraceae Actinotrichia fragilis (Forsskål) Børgesen
Dichotomaria australis (Sonder) Huisman, J.T. Harper & G.W. Saunders
Dichotomaria marginata(Ellis & Solander) Lamarck
Dichotomaria obtusata(Ellis & Solander) Lamarck
Galaxaura divaricata(Linnaeus) Huisman & Townsend
Galaxaura filamentosa R. Chou
Galaxaura obtusata(Ellis & Solander) Lamouroux
Galaxaura rugosa(Ellis & Solander) Lamouroux
Tricleocarpa fragilis(Linnaeus) Huisman & Townsend
Order Nemaliales
Family Liagoraceae Liagora sp.
Yamadaella caenomyce(Decaisne) I.A. Abbott
Order Nemaliales
Family Scinaiaceae Scinaia furcata Zablackis
Order Plocamiales
Family Plocamiaceae Plocamium sandvicense J. Agardh
Plocamium sp.
Order Rhodymeniales
Family Champiaceae Champia compressa Harvey
Champia parvula (C. Agardh) Harvey
Champia vieillardii Kützing
Order Rhodymeniales
Family Faucheaceae Gloiocladia iyoensis (Okamura) R. Norris
Order Rhodymeniales
Family Lomentariaceae Lomentaria corallicola Børgesen
Order Rhodymeniales
Family RhodymeniaceaeAsteromenia anastomosans(Weber-van Bosse) G.W. Saunders,C.E. Lane, C.W. Schneider & Kraft
Asteromenia pseudocoalescensG.W. Saunders, C.E. Lane,C.W. Schneider & Kraft
Botryocladia kuckuckii(Weber-van Bosse) Yamada & Tanaka
Botryocladia skottsbergii(Børgesen) Levring
Botryocladia spinuliferaW.R. Taylor & I.A. Abbott
Chamaebotrys boergesenii(Weber-van Bosse) Huisman
Chrysymenia procumbensWeber-van Bosse
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The Natural History of Santo
Coelothrix irregularis(Harvey) Børgesen
Gelidiopsis intricata (C. Agardh) Vickers
Gelidiopsis repens(Kützing) Weber-van Bosse
Gelidiopsis scoparia(Montagne & Millardet) De Toni
Halichrysis irregularis(Kützing) A.J.K. Millar
Leptofauchea sp.
Rhodymenia intricata(Okamura) Okamura
Rhodymenia pacifica Kylin
Rhodymenia sp. 1
Rhodymenia sp. 2
class chlorophyta
Order Bryopsidales
Family BryopsidaceaeBryopsis pennata J.V. Lamourouxvar. secunda (Harvey) Collins & Hervey
Order Bryopsidales
Family Caulerpaceae Caulerpa biserrulata Sonder
Caulerpa brachypus Harvey
Caulerpa cupressoides(Vahl) C. Agardh
Caulerpa fastigiata Montagne
Caulerpa fergusonii Murray
Caulerpa manorensis Nizamuddin
Caulerpa microphysa(Weber-van Bosse) Feldmann
Caulerpa nummulariaHarvey ex J. Agardh
Caulerpa racemosa (Forsskål) J. Agardhvar. clavifera Turner (Weber-van Bosse)
Caulerpa racemosa (Forsskål) J. Agardh var. lamourouxii (Turner) Weber-van Bosse
Caulerpa racemosa (Forsskål) J. Agardhvar. peltata (Lamouroux) Eubank
Caulerpa sedoides C. Agardh
Caulerpa serrulata (Forsskål) J. Agardh
Caulerpa sertularioides(S. Gmelin) M. Howe
Caulerpa taxifolia (Vahl) C. Agardh
Caulerpa verticillata J. Agardh
Caulerpa webbiana Montagne
Caulerpella ambigua (Okamura) Prud'homme van Reine & Lokhorst
Order Bryopsidales
Family Codiaceae Codium arabicum Kützing
Codium geppiorum O.C. Schmidt
Codium mamillosum Harvey
Codium ovale Zanardini
Order Bryopsidales
Family Halimedaceae Halimeda borneensis W.R. Taylor
Halimeda cuneata K. Hering
Halimeda cylindracea Decaisne
Halimeda discoidea Decaisne
Halimeda distorta(Yamada) Hillis-Colinvaux
Halimeda gigas W.R. Taylor
Halimeda heteromorpha N'Yeurt
Halimeda lacunalis (W.R. Taylor) Hillis
Halimeda macroloba Decaisne
Halimeda macrophysa Askenasy
Halimeda micronesica Yamada
Halimeda minima(W.R. Taylor) Colinvaux
Halimeda opuntia(Linnaeus) Lamouroux
Halimeda taenicola W.R. Taylor
Order Bryopsidales
Family PseudocodiaceaePseudocodium floridanumDawes & Mathieson
Order Bryopsidales
Family UdoteaceaeAvrainvillea erecta(Berkeley) A. Gepp & E. Gepp
Avrainvillea lacerataHarvey ex J. Agardh
Boodleopsis pusilla(Collins) W. Taylor, Joly & Bernatowicz
Chlorodesmis fastigiata(C. Agardh) Ducker
Chlorodesmis hildebrandtiiA. Gepp & E. Gepp
Rhipidosiphon javensis Montagne
Rhipilia crassa A.J.K. Millar & G.T. Kraft
Rhipilia penicilloides N'Yeurt & Keats
Rhipilia sinuosa Gilbert
Rhipilia sp. nov.
Rhipiliopsis carolyniae Kraft
Rhipiliopsis echinocaulos(A.B. Cribb) Farghaly
358. . .
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Valonia macrophysa Kützing
Valonia ventricosa J. Agardh
Valoniopsis pachynema(G. Martens) Børgesen
Order Ulvales
Family Ulvaceae Ulva intestinalis (Linnaeus) Nees
Ulva lactuca Linnaeus
class phaeophyceae
Order Dictyotales
Family DictyotaceaeDictyopteris repens(Okamura) Børgesen
Dictyopteris sp.
Dictyota bartayresiana Lamouroux
Dictyota ceylanica Kützing
Dictyota cf. canaliculata O. De Clerck & E. Coppejans
Dictyota cf. friabilis Setchell
Dictyota cf. pfaffii Schnetter
Dictyota divaricata Lamouroux
Dictyota friabilis Setchell
Dictyota grossedentataDe Clerck & Coppejans
Dictyota hamifera Setchell
Dictyota sp.
Distromium sp.
Lobophora papenfussii(W.R. Taylor) Farghaly
Lobophora variegata (Lamouroux) Womersley ex Oliveira
Padina boryana Thyvi
Padina melemeleAbbott & Magruder in Abbott
Padina sp.
Padina sp. nov.
Stypopodium flabelliformeWeber-van Bosse
Order Ectocarpales
Family Acinetosporaceae Hincksia indica (Sonder) J. Tanaka
Order Fucales
Family SargassaceaeSargassum aquifolium(Turner) C. Agardh
Spatoglossum asperum J. Agardh
Turbinaria ornata (Turner) J. Agardh
Order Sphacelariales
Family Sphacelariaceae Sphacelaria tribuloides Meneghini
Rhipiliopsis howensis Kraft
Siphonogramen sp.
Tydemania expeditionisWeber-van Bosse
Udotea argentea Zanardini
Order Cladophorales
Family Anadyomenaceaea Anadyomene wrightii Harvey ex J. Gray
Microdictyon umbilicatum(Velley) Zanardini
Order Siphonocladales
Family BoodleaceaePhyllodictyon anastomosans(Harvey) Kraft & M.J. Wynne
Order Cladophorales
Family CladophoraceaeChaetomorpha antennina(Bory de Saint-Vincent) Kützing
Cladophora dotyana Gilbert
Cladophora glomerata (L.) Kutzing
Cladophora liebetruthii Grunow
Cladophora ohkuboana Holmes
Cladophora prehendens Kraft & Millar
Cladophora sp.
Order Siphonocladales
Family SiphonocladaceaeBoergesenia forbesii(Harvey) J. Feldmann
Order Dasycladales
Family Dasycladaceae Bornetella nitida Sonder
Bornetella sphaerica(Zanardini) Solms-Laubach
Neomeris vanbosseae Howe
Order Siphonocladales
Family Boodleaceae Boodlea composita (Harvey) F. Brand
Cladophoropsis herpestica(Montagne) M.A. Howe
Cladophoropsis vaucheriaeformis(J.E Areschoug) Papenfuss
Struvea elegans Børgesen
Order Siphonocladales
Family SiphonocladaceaeDictyosphaeria cavernosa(Forsskål) Børgesen
Dictyosphaeria intermediaWeber-van Bosse
Dictyosphaeria versluysiiWeber-van Bosse
Siphonocladus sp.
Order Siphonocladales
Family Valoniaceae Valonia aegagropila C. Agardh
Valonia fastigiata Harvey ex J. Agardh
. . . . . . .
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The Natural History of Santo
Figure 423: rhodophyta. a: Amansia rhodantha. b: Amphiroa crassa. c: Amphiroa foliacea. d: Asteronemia anastomosans. e: Botryocladia spinuligera. F: Callophycus serratus. g: Cheilosporum spectabile. h: Corallinales complex. (Photos J.-L. Menou Ird Nouméa).
a B
C d
E F
g h
360. . .
. . . . . . .Marine Ecosystems
Figure 424: rhodophyta. i: Dasyphila plumarioides. J: Dichotomaria marginata. K: Dichotomaria obtusata. l: Galaxaura divaricata. m: Gibsmithia hawaiiensis. n: Halymenia porphyraeformis. o: Halymenia stipitata. p: Lithothamnion proliferum. (Photos J.-L. Menou Ird Nouméa).
I J
K L
M N
o P
. . . . . . .
. . .361
The Natural History of Santo
Figure 425: rhodophyta. Q: Martensia flabellata. r: Martensia sp. nov. S: Neogoniolithon fosliei. t: Peyssonnelia inamoena. U: Plocamium sandvicense. v: Portieria hornemanii. W: Predaea laciniosa. X: Titanophora weberae. (Photos J.-L. Menou Ird Nouméa).
W X
u V
s t
rQ
362. . .
. . . . . . .Marine Ecosystems
Figure 426: Chlorophyta. a: Caulerpa bisserulata. b: Caulerpa fergusoni. c: Codium mamillosum. d: Halimeda cuneata. e: Halimeda discoidea. F: Halimeda lacunalis. g: Halimeda macroloba. h: Halimeda minima. (Photos J.-L. Menou Ird Nouméa).
h
FE
g
dC
Ba
. . . . . . .
. . .363
The Natural History of Santo
Figure 427: Chlorophyta. i: Halimeda taenicola. J: Avrainvillea erecta. K: Rhipilia sp. l: Tydemania expeditionis. m: Cladophora ohkuboana. n: Bornetella nitida. o: Cladophorospsis herpestica. p: Valonia ventricosa. (Photos J.-L. Menou Ird Nouméa).
I J
K L
M N
o P
364. . .
. . . . . . .Marine Ecosystems
Figure 428: Phaeophyceae. a: Dictyota barteyresiana. b: Dictyota ceylanica. c: Dictyota friabilis. d: Distromium sp. e: Padina boryana. F: Padina melemele. g: Padina sp. h: Stypopodium. (Photos J.-L. Menou Ird Nouméa).
a B
C d
E F
g h
. . . . . . .
. . .365
The Natural History of Santo
algal assemblages …••• Algal vegetation on outer reefs and slopes
down to 20 mThe algal community on the outer reef and slope down to 20 m in depth comprises a large number of encrusting coralline algae mixed with several dozen species growing among corals. Near the top of the reef, many species — mainly red algae — grow within the interstices of corals, and include Chondrophycus parvipapillatus, Avrainvillea lacerata, Martensia flabelliformis, Halymenia porphyraeformis, Meristotheca procum-bens, Champia vieillardii, Caulerpa nummularia, C. biserrulata and Halimeda micronesica. In the break-water area coralline algae Hydrolithon onkodes and Neogoniolithon fosliei develop thick candle-like crusts, with Hydrolithon orthoblatum or branched clumps of Lithophyllum pygmaeum. The vegetation can vary according to the topography and the presence of gutters and grooves is often associ-ated with large clumps of Callophycus serratus, Cheilosporum spectabile, Asparagopsis taxiformis, Dasyphila plumarioides, Tricleocarpa fragilis, Caulerpa spp. and Halimeda spp. and small species such as Chondria armata, Botryocladia spp., Chamaebotrys boergesenii and Portieria hornemanii. The pinkish colours of coralline algae contrast with
the very bright green pompom-like morphology of Chlorodesmis hildenbrandtii and Rhipilia penicilloides. Further down the reef slope, from 8-20 m deep, the motion of the water is reduced and the reefs sup-port a higher coral cover and articulated calcareous algae such as Amphiroa crassa, A. tribulus and A. foliacea, and the green Halimeda cuneata, H. gigas, H. minima and H. taenicola dominate some reef slopes. Fleshy algae are less abundant and mostly comprise Gibsmitha hawaiiensis, Amansia rhodanta and Valonia
0 5 10 15 20 25 30
PseudocodiaceaeAnadyomenaceaea
UlvaceaeCodiaceae
DasycladalesDasycladaceae
BoodleaceaeSiphonocladaceae
ValoniaceaeCladophoraceae
HalimedaceaeUdoteaceae
Caulerpaceae
AcinetosporaceaeSargassaceaeDictyotaceae
BonnemaisoniaceaeCaulacanthaceae
CorynocystaceaeaDicranemataceaeSchizymeniaceae
ScinaiaceaePlocamiaceaeFaucheaceae
LomentariaceaeNemastomataceae
RhizophyllidaceaGracilariaceaeSebdeniaceae
LiagoraceaeChampiaceae
GelidiaceaePeyssonneliaceae
DasyaceaeHypneaceaeSolieriaceae
DumontiaceaeHalymeniaceaeGalaxauraceaeDelesseriaceae
CeramiaceaeCorallinaceae
RhodymeniaceaeRhodomelaceae
Fam
ilies
number
Figure 429: species richness of the families of rhodophyta (red), Phaeophyceae (brown) and Chlorophyta (green).
Bryopsidales
Cladophorales
Siphonocladales
Ulvales
Dictyotales
Ectocarpales
Fucales
Bonnemaisoniales
Ceramiales
Corallinales
Gelidiales
Gigartinales
Figure 430: repartition of the algal community in orders rhodophyta (red), Phaephyceae (brown), Chlorophyta (green).
366. . .
. . . . . . .Marine Ecosystems
fastigiata. Rubble is often found at the bottom of the slope rupture, at ~ 15 m deep and Caulerpa serru-lata, C. sedoides, Microdictyon umbilicatum, Neomeris van-bossea, Halimeda distorta, Valonia aegagropila, Myriogramme melanesiensis, Stypopodium flabelli-forme and Padina spp. grow among the coral debris. Various thin and small fronds of dark green Rhipilia spp. and Rhipiliopsis spp., Anadyomene wrightii form small associations in the shady areas with Corynocystis protrata and Cryptonemia crenulata.
••• Algal vegetation on deep outer slopesIn the outer slope from 40 m to at least 60 m deep, coral debris and coarse sand dominate the substra-tum. At the first glance fleshy algae are relatively few in species number and the vegetation is not luxuriant. Most of the gelatinous red algae such as Dudresnaya capricornica, Predaea weldii, P. laciniosa, Gibsmithia hawaiiensis, G. larkumii, and the green algae Caulerpa fergusonii, C. sedoides, C. micro-physa, Codium mamillosum, Rhipilia sp. nov. grow in this environment on and among the coral debris, while the delicate green Cladophora ohkuboana, C. dotyana are found on sand. Brown algae are very few and Dictyota bartayresiana and Padina groupe melemele can be observed in this deep habitat.
••• Algal vegetation on coral wallsCoral walls usually start deeper than 30 m on the edge of limestone islands located in deep open water. This environment is often dark due to a heavily vari-egated surface with numerous interstices, overhangs and small caves. Coral walls are of great beauty with spectacular encrustations by coralline algae and Peyssonnelia spp. giving an attractive mosaic of forms and colours. The dominant Lithothamnion prolifer is easily recognisable by its pink crust and numer-ous short knobs. Numerous Rhodymeniales includ-ing several species of Leptofauchea and Rhodymenia live in the caves and interstices with Cryptonemia crenulata, C. umbraticola, Corynocystis prostrata and Callophycus serratus, while the iridescent Halichrysis irregularis and the star-like Asteromenia anastomo-sans grow luxuriantly on the walls with the large foliose Peyssonnelia inamoena and P. capensis. The golden-yellow Padina melemele and the green ball-like Codium mamillosum are present in discrete clumps among coral debris with very occasional Sebdenia flabellata and S. cerebriformis.
All these species can be found in other deep areas but in less abundance. The shady environment and open ocean influences enhance this algal community that is generally sheltered in the reef interstices.
••• Algal vegetation on the sandy bottomof deep lagoons
Various green algae grow together and develop meadows between coral colonies located on the coral sandy bottom at 25-30 m deep in the embayments.
This sheltered and silty environment supports luxuriant vegetation including: Udotea argentea, Avrainvillea erecta, Halimeda borneensis, H. distorta, Caulerpa verticilata, C. cupressoides, C. racemosa, C. sedoides, C. serrulata, C. taxifolia as well as some red algae such as Martensia, Titanophora webera and the brown alga Stypopodium flabelliforme with its fan-like shape and iridescent blue on the thallus surface.
••• Algal vegetation on shallow reef flatsThe shallow fringing reef flat along the shoreline to the north of Luganville supports many algae from the beach to the reef front. The flats are exposed at low tide and corals are therefore reduced in abundance, except at the outer part of the reef flat where large stands of staghorn Acropora grow in the gutters per-pendicular to the reef front. Adjacent to the beach, the reef is covered with a green underwater "turf" mainly composed of Cladophora glomerata, Boodlea composita and Boergesenia forbesii that is partially buried in the sand. Several Caulerpa, C. fastigiata, C. racemosa, C. serrulata along with light green Chlorodesmis fastig-iata, Halimeda opuntia and the red pompom-like algae Galaxaura filamentosa and G. rugosa grow on the inner part of the reef. Among the coral branches there are numerous green algae Dictyosphaeria cavernosa and H. micronesica. The edible red seaweed Meristotheca procumbens was abundant within the coral branches and in the interstices on the reef margin. The vegeta-tion on the front part is dominated by nongeniculated coralline algae including crusts of Hydrolithon onkodes and the candle-like thallus of H. orthoblastum. Various articulated coralline algae such as Amphiroa spp. form clumps on the reef top. Surprisingly, no stands of Sargassum were observed except occasional young stages of Sargassum aquifolium.
••• Algal vegetation in shallowsandy coral communities
The algal vegetation associated with the coral com-munity in shallow sandy environments is mainly rep-resented by patches of the fan-like brown alga Padina boryana mixed with another brown alga Turbinaria ornata and various species of green algae such as Caulerpa cupressoides, C. racemosa, C. racemosa var lamourouxii, C. fergusonii, Boodlea composita and Udotea argentea and the red algae Galaxaura rugosa, Hypnea spp. and Tolypiocladia glomerata. Microdictyon umbilicatum, Halimeda discoidea and Myriogramme melanesiensis grow among the branches of staghorn Acropora. Moreover, the delicate red algae Martensia fragilis, Neomartensia flabelliforme, Haloplegma dup-pereyi, along with Laurencia spp., Exophyllym wentii and several Rhodymeniales form small associations of a rich algal flora in the interstices of submassive corals Porites rus and Montipora.
••• Algal vegetation in channel environmentsIn general, the algal vegetation of the channels is not very rich due to the silty and muddy environment that
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The Natural History of Santo
limits algal diversity. There is no typical association of algae from this environment except the brown alga Spatoglossum asperum which has only been recorded in the Segond Channel and Malo passage. The algal flora has characteristics that are typical of sheltered areas; Halimeda spp. and Caulerpa spp. can locally cover the substratum and most of the investigated sites showed coral damage. The algal vegetation asso-ciated with dead coral communities is described in the next section.
••• Algal vegetation on dead coral communitiesSanto coral reefs have experienced heavy damage from successive cyclones, bleaching events and crown-of-thorns starfish (Acanthaster) outbreaks in the past decades. Thus on the outer reefs and slopes along the channel, the dead corals are colonized by small prostate algae such as the brown Dictyota fria-bilis, Lobophora variegata and large green calcareous Halimeda distorta and H. minima. In more exposed locations, dead and collapsing branches are over-grown by coralline algae, turfs of filamentous red algae and cyanobacteria assemblages. Depending on the local environmental and reef condition, this pioneer stage of colonization will evolve into a sec-ondary succession of algal-dominated communities or revert to coral recolonization.
••• Remarks on the absence of Sargassum bedsSargassum species are common features of the algal vegetation of tropical islands in the Pacific. However, around Santo this genus is restricted to limited germ-lings and the reduced thalli of Sargassum aquifolium on reef flats, while personal observations in Efate at the same period have shown the presence of large beds of Sargassum including several common tropical species such as S. polycystum. The lack of suitable habitats such as sheltered shallow lagoons could explain the absence of the species in these biotopes around Santo.
Seagrass communities …Seagrasses are flowering plants belonging to the Cymodoceaceae and the Hydrocharitaceae families which are placed in the Alismatales order (nomen-clature based on molecular analysis). In tropical regions they are mostly permanently submerged
in marine and estuarine biotopes that are gener-ally sheltered from wave action and offer a suitable substratum for rooting in mud, sand or coarse rub-ble. In many places they can also develop into large meadows or beds in deeper lagoon zones down to 40 m deep, on barrier reefs or surrounding lagoon islands. They are remarkable habitats in tropical shallow waters and they often form a key func-tioning system on sandy bottoms along shorelines between mangroves and coral reefs.
Most coastal areas around Santo do not have these typical seagrass habitats and only the fringing sandy flats adjacent to estuarine and river catch-ments, sheltered embayments and inner reef sandy flats provide the necessary conditions for seagrass development. However, deep sandy slopes, sandy channel slopes and bottoms also support the pad-dle-like Halophila seagrasses.
Eight species of seagrass were reported from our survey (Table 38), four of these are new records for Santo: Cymodocea serrulata, Enhalus acoroides, Halophila capricorni and H. decipiens, and the two species of Halophila had not been previously recorded for the Vanuatu archipelago.
Seagrass diversity and abundance were relatively low in the investigated areas. Plants never form large meadows; they mostly developed in scattered patches except in Palikolo bay where they form dense mats (> 75 % coverage) in 70 m wide zones that repre-sent the most extensive bed surveyed. The seagrass communities generally comprised few species; most of the sites had just one to three species growing together. The inner sandy areas such as Palikolo bay, the Aore shoreline in the Malo passage and the estuarine zone adjacent to Luganville showed the highest species diversity with four species growing together. However, most of the time one species was dominant in the bed, i.e. Halodule uninervis in Luganville, Cymodocea rotundata in Palikolo. In some localities seagrasses form mixed communities with marine algae such as Halimeda macroloba, H. cylindracea, H. borneensis, Caulerpa serrulata, Padina boryana and Acanthophora spicifera.
class order Family genus Species authority
Anthophyta Alismatales Cymodoceacea Cymodocea rotundata (Hemprich & Ehrenberg) Aschers & Schweinf
Cymodocea serrulata (R. Brown) Aschers & Magnus
Halodule uninervis (Forsskål) Ascherson in Boissier
Hydrocharitacea Enhalus acoroides (Linnaeus) Royle
Halophila capricorni Larkum
Halophila decipiens Ostenfed
Halophila ovalis (R. Brown) J.D. Hooker
Thalassia hemprichii (Ehrenberg) Ascherson
table 38: List of seagrass species from santo waters.
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Except for the species of Halophila, all the other taxa were confined to very shallow waters although they are known to grow in deeper habitats elsewhere.
It is clear that the coastal physiography of Santo does not provide ideal habitats for seagrass mead-ows, but it is not clear why seagrasses are so restricted in shallow waters and are not well devel-oped in other areas that appear to be suitable. Part of the explanation could be due to climatic condi-tions. The high occurrence of cyclones and rough seas can provoke sediment movements and salinity
changes, which may have prevented the establish-ment of seagrasses or removed beds which would both have limited the development or the absence of this key functioning habitat. This situation could turn critical with the predicted increase of threats as a result of human activities and climate change. Seagrass habitats must be considered as associated ecosystems to coral reefs just like mangroves. All these habitats are important and integral compo-nents of the natural environment of Santo and they must be considered as priorities in conservation efforts. This study provides information that could aid coastal zone planning and development.
Figure 431: seagrass species. a: Cymodocea serrulata. b: Halodule uninervis. c: Enhalus acoroides. d: Thalassia hemprechii. e: Halophila capricorni. (Photos J.-L. Menou Ird Nouméa).
a B
C d
E